CA1126392A

CA1126392A - Memory type automatic adjustment system

Info

Publication number: CA1126392A
Application number: CA297,422A
Authority: CA
Inventors: Eiji Tamura; Takashi Nakamura
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1977-02-28
Filing date: 1978-02-21
Publication date: 1982-06-22
Also published as: US4274107A; DE2808600A1; JPS53106520A; AU3364778A; FR2382139B1; GB1551700A; IT1102708B; FR2382139A1; ATA144178A; NL7802191A; DE2808600C2; AU513836B2; AT379046B; IT7848201A0; JPS6048955B2

Abstract

ABSTRACT OF THE DISCLOSURE

A memory-type control system for producing and storing a control signal which is used in an automatic adjustment system.
A signal, having a parameter to be controlled, is provided; and a detecting circuit detects when the parameter is within a pre-determined range. An UP/DOWN counter counts clock pulses and is responsive to the detecting circuit for counting in one direc-tion when the detected parameter is greater than the predetermined range, for counting in a second direction when the detected para-meter is less than the predetermined range and for ceasing its counting when the detected parameter is within the predetermined range. A parameter control circuit uses the count of the counting means as a control signal to adjust the parameter so as to bring said parameter within the predetermined range. A typical applica-tion of the automatic adjustment system is a white-balance control system for use with video camera apparatus.

Description

~263~2 ~CKGROUND OF THE INVENTION
This invention relates to a memory-type automatic adjustment system and, more particularly, to such a system wherein a particular parameter of a signal, such as the gain of a signal, is automatically controlled. A preferred applica-tion of the present invent;on is in a white balance adjustment circuit for a video camera.
In some automatic adjustment systems, an input signal or signals is controlled in accordance with a predetermined or desired condition. For example, in an automatic gain control system, the gain of an input signal is controlled in accordance with a reference level such that if the input signal level or the reference level varies, a corresponding adjustment is made in the gain of the controlled signal. Often, the condition upon lS which an adjustment is made is not continuous. Rather, a deter-mination of a proper control signal may be made during one time period and this determined control signal then may be stored for future time periods in order to effect an automatic adjustment operation.
The foregoing type of an automatic adjustment or control operation advantageously utilizes a memory-type control device.
One such use of the memory-type control device is in an automatic white balance adjustment system for a video camera. In a color television camera, a proper white balance is achieved when the individual color signals are of predetermined amplitudes, or levels, when a white object is viewed by the camera. However, even if the white balance of the camera is set or adjusted to be correct for one color temperature of an object, this white balance may be lost or ot~erwise degraded in the event that the color temperature of illumination ~or the object changes~ A loss ~J.Z~3~2 of the white balance condition also may arise when the operating temperature of the electrical apparatus included in the camera changes, or due to other changes in the electrical components over long periods of tlme. Accordingly, to account for these changes, it often is necessary to update the white balance of the color video signals, and then to use the updated, balanced signals to control the respective gains of the color signals.
In controlling the white balance of color video signals, a white object is viewed, for example, a white wall, board, or other reference object, and the gains, or levels, of the respec-tive color signals which are produced in response to the viewed white object are adjusted until proper white balance is attained.
The control signals which ultimately result in the proper white balance are stored and are used as gain control signal.s when the camera apparatus views other objects, such as a ~elevised scene.
When the white balance cLanges, or is expected to change, because of the above-mentioned conditions, the gain control signals are updated by performing again the aforementioned white balance opera-tion.
One type of white balance control system which is effec-tive in controlling the white balance of color video signals is disclosed in U.S. Reissue Pat. Wo. 28,774. In that system, color difference signals, such as the red (R-Y) and blue (B-Y) color difference signals are integrated and supplied tc respective memory circuits for controlling the gains of the red and blue video signals which are produced by the color camera. When proper white balance is attained, the color difference signals R-Y and B-Y each are zero. This zero level establishes the proper gain of the respective red and blue gain control circuits. In the event that the white balance is lost, a corresponding color ~J.~63~2 difference signal voltage is produced and is used to adjust the gai,ns of the red and blue signals in a direction so as to restore the white balance. The signal levels which are used to establish the gains of the red and blue gain control circuits so as to pro-vide proper white balance are stored. Hence, when the camera isused to televise a scene other than a reference white object, the televised scene likewise will have a proper white balance in accord-ance with the stored control signals. In another embodiment of the white balance control system disclosed in this patent, red-green (R-G) and blue-green (B-G) color difference signals are used to determine whether proper white balance of a viewed white reference object is achieved. That is, the R-G and B-G s~gnals are used to adjust the respective gains of the red and blue signals such that the difference between the gain-controlled red and blue signals and the green signal result in correct white balance. The control signals which attain this proper balance are stored and used to establish the gains of the red and blue signals when the video camera apparatus is used to view a televised scene.
In yet another type of white balance control system, white balance is achieved by using the camera to view a white reference object and then to control the level of the luminance component Y in such a manner that the color difference signals R-Y and B-Y, derived from the viewed white object, each are zero.
The control signals which result in proper white balance then are stored and used to control the gain of the luminance component for further usage of the video camera.
In the white balance control systems of the type described above, the control signals, such as the gain control signals, which must be stored and used when the camera televises a normal scene generally arestored by a memory circuit constituted by a capacitor.

~.263~

However, as is known, a capacitor usually is accompanied by leakage, whereby the level of a signal stored thereacross is degraded, or reduced, over prolonged periods of time. Hence, although the control s;gnal stored across the capacitor initially will be correct to achieve proper white balance, the leakage of this signal soon will result in a loss of white balance. This means that frequent readjustments in white balance are necessary.
Another type of memory-type white balance control system is described in NEC Research and Development Bulletin, No. 40, January 1976, wherein an UP/DOWN counter is used to derive and store a digital control signal which is converted to an analog gain control signal. However, this publication does not describe how the UP/DOWN counter is controlled other than by suggesting that red-green and blue-green difference signals are used.
OBJECTS OF THE INVENTION
.
Therefore, it is an object of the present invention to provide an improved memory-type automatic adjustment system.
Another object of this invention is to provide a memory-type gain control system which avoids the disadvantages attending prior art memory-type gain control systems.
A further object of this invention is to provide a memory-type automatic adjustment system which uses a digital counter for deriving and storing a gain control signal.
An additional object of this invention is to provide a memory-type white balance control system for use in video camera apparatus.
Yet another object of this invention is to provide a memory-type white balance control system wherein ~ digital counter is used to derive and produce a control signal based upon the devia-tion of a color difference signal from a predetermined range.

63~

Various other objects, advantage and features of the present invention will become readily apparent from the ensuing de~ailed description, and the novel features will be particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
In accordance with this invention, a memory-type control system is provided for producing and storing a control signal which is used to automatically adjust a predetermined parameter of an input signal. A detecting circuit detects when the predetermined parameter is within a preset range. An UP/DOWN counter counts clock pulses in a first direction when the parameter is detected as being greater than said preset range and counts in a second direction when the parameter is detected as being less than said preset range. The UP/DOWN counter ceases its counting when the parameter is detected as being within the preset range. The count of the counter is used as a control signal for adjusting the pre-determined parameter in a manner so as to bring that parameter within the preset range.
In one application of the aforedescribed memory-type control system, the system is used as a white balance control system for controlling the white balance of color video signals produced by video camera apparatus. In that system, the input signal is a color difference signal and the parameter thereof which is controlled is the level of the color difference signal.
The white balance control system is made operative when the camera views a white object; and the parameter adjustment circuit is an automatic gain control circuit which controls the level of a com-ponent included in the color difference signal, which component is fed back to and combined with the color difference signal, whereby the level of the combined signal is controlled to effect a proper white balance.

~.Z,63~%

More particularly, ther~ is prGvided:
A memory-type control system for producing and storing a control signal, comprising:
signal providing means for providing a signal having a level to be controlled;
detecting means for receiving said signal for detecting when said level is within a predetermined range;
a source of clock pulses;
UP/DOWN counting means for counting said clock p~llses, s2id rJP/DOW~I counting means being responsive to said detecting means for counting in one direction when said level is greater than said predetermined range, for counting in a second direction when said level is less than said predetermined range and for ceasing said counting when said level is within said range so as to store the last-attained count;
level control means coupled to said counting means for using said count as a control signal to adjust said level so as to bring said level within said predetermined range;
preset means for presetting said counting means with 2 predetermined count; and switch means having a first condition to inhibit sald counting means and being operable to a second condition to load said counting means with said predetermined count and to enable said counting means for initiating a level adjustment operation by said detecting means, said counting means and said level control means.
There is also provided:
~ memory-type white balance control system for controlling the white balance of color video signals ~roduced by video camera apparatus, comprising:

- 5a -63~
means for producing first and second color difference signals corresponding to an object viewed by said camera apparatus;
means for producing a component of said color difference signals;
sensing means responsive to the level of said component for sensing when the object viewed by said camera is a white o~ject;
first and second combining means for combining said component with said first and second color difference signals, respectivel~, to prodace first and second white-balanced color difference signals;
first and second sampling means responsive to said sensing means for sampling said first and second white-balanced color difference signals, respectively;
first and second range comparators for determining if said first and second sampled white-balanced color difference signals are within first and second amplitude ranges, respectively, to produce first and second count-down signals if said first and second sampled white-balanced color difference signals exceed the upper limits of said first and second ranges, respectively, first and second count-up signals if said first and second sampled white-balanced color difference signals are less than the lower limits of said first and second ranges, respectivel~, and stop signals if said first and second sampled white-balanced color difference signals are within said`
first and second ranges, respectively;
a source or clock pulses;
first and second UP/DOWN counting means for counting ~
said clock pulses, said first and second counting means being responsive to said first and second count-down, count-up and stop signals, respectively, for counting in a downward direction, counting in an upward direction and stopping said counting;

A - 5b -63~2 first and second automatic gain control means responsive to the ccunt of said first and second counting ~eans, respectively, for controlling the level of sai.d component which is combined with a respective one of sald firs' and second color difference signals; and indicating means responsive to said first and second stop signals for indicating when said first and second white-balanced color difference signals are balanced properly.
There is further provided:
A memory-type control system for producing and storing 3 control signal, comprising:
signal providing means for providing a signal having a level to be controlled;
detecting means receiving said signal to be controlled for detecting when said level is within a pre-determined range;
a source of clock pulses;
UP/DOWN counting means for counting said clock pulses, sa.id UP/DOWN counting means being responsive to said detecting means for counting in one direction when said level is greater than said predetermined range, for counting in the other direction when said level is less than said predetermined range and for ceasing said counting when said level is within said range so as to store the last-attained count;
level control means coupled to said counting means and using said count as a gain control signal to adjust said level so as to bring said level within said predetermined range, said level control means including level adjusting means fo- ~djusting the level of said signal, and digital-to-analog conv~rting means for converting the count of said counting means to an analog level control signal and for applying said analog level control signal to said level adjusting means; and - 5c -63~Z

said signal providing means including a source of color video signals representing a white object, means for deriving a color difference signal corresponding to said white object, means for providina a component of said color difference signal, and means for aLgebraical].y combining said component and said color difference signal so as to vary the level of said color difference signal, said component being applied to said algebraic combining means tnrough said level adjusting means.

- Sd -~., l~l.Z63~;~

BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description, given by way of example, will best be understood in conjunction with the accom-panying drawings in which:
FIG. 1 is a block diagram showing one application of the present invention to a white balance control system;
FIG. 2 is a diagram of a televised object which is useful in understanding the operation of the system shown in FIG. l;
FIGS. 3A-3D are waveform diagrams which are helpful in understanding the operation of the system shown in FIG. l;
FIG. 4 is a logic diagram of one embodiment of a memory-type adjustment system in accordance with the present invention;
FIG. 5 is a graphical representation which is useful in understanding the operation of the counter used in the embodi-ment shown in FIG. 4; and FIG. 6 is a logic diagram of another embodiment of a memory-type adjustment system which can be used as a white balance control system.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
The present invention, now to be described, finds general application as a memory-type adjustment system, such as a memory-type gain control device. Notwithstanding the general application of this invention, it will be described in the environment of an intended application thereof as a memory-type white balance control system. However, it should be readily understood that this inven-tion need not be lim;ted solely to this environment. Those of ordinary skill in the art readily will appreciate that this inven-tion can be used as, and is contemplated for use in, various types of adjustment systems wherein a control signal is to be stored for prolcnged periods of time.

~I.Z63~Z

Turning now to FIG. 1, there is illustrated a white balance adjustment system for use with video camera apparatus and with which the memory-type control system of the present invention can be employed. The video camera apparatus shown herein is the two-tube type color camera; but, as will be appre-ciated, the camera apparatus alternatively could be a one-tube, a three-tube or a four-tube camera. An optical lens 2 is in optical communication with a camera tube 3 and with a camera tube 6. A half-mirror 5, or other beam-splitting device, serves to transmit a portion of the video image focused by lens 2 through to camera tube 3 and to reflect a portion of the video image to camera tube 6. Camera tube 3 is adapted to produce color video signals and to supply such color video signals to a conventional color decoder 4. In this respect, camera tube 3 is conventional and may comprise a vidicon tube having a color coding filter. The color decoder functions to produce color difference signals from the color signals supplied thereto by camera tube 3. As an example, color decoder 4 produces red (R-Y) and blue (B~Y) color difference signals, wherein the component Y
of the color difference signals is the luminance component. Although not shown herein, for the purpose of white balance, the color differ-ence signals produced by color decoder 4 may be the R-G and B-G
color difference signals, wherein R, B and G are the red, blue and green video signals, respectively.
A synchronizing signal generator 9 is coupled to camera tubes 3 and 6 to supply horizontal and vertical drive signals HD
and VD thereto. These drive signals scan electron beams across target plates of the camera tubes in the horizontal and vertical direction~, as is conventional. Hence, the color signals produced by camera tube 3 are the color signals o ~he object which is ~J.~63~}2 imaged by lens 2 and half-mirror 5 onto the camera tube. Similarly, the video signalsproduced by camera tube 6 are the luminance signals of the object which is imaged onto the camera tube by lens 2 and half-mirror 5.
As is appreciated, camera tubes 3 and 6 need not neces-sarily include a scanning electron beam. Nevertheless, synchroniz-ing signal generator 9 supplies synchronizing drive signals to these c ~ ra tubes to produce proper color difference and luminance si~nals therefrcm.The luminance signal produced by camera tube 6 is supplied to a processing circuit 7, such as a gamma corrector, from which the luminance component Y is derived. This luminance component Y
is derived from an output terminal 8 for use in a conventional color encoder (not shown) whereby color video signals are encoded for transmission. As one example, the color encoder may be an NTSC-type encoder. As another example, the color encoder may be a PAL-type encoder.
The color difference si~nals produced by color decoder 4, shown herein as R-Y and B-Y color difference signals, are supplied to respective channels 20R and 20B for the purpose of white balance adjustment. That is, channels 20R and 20B are operable to modify the respective color difference signals in a manner such that these color difference signals are properly balanced when the video camera apparatus views a white object. In particular, when a white object is viewed by the camera apparatus, the respective color difference signals R-Y and B-Y should be zero. If white balance is lost, this J
zero condition will not be attained. The purpose of channels 20R
and 20B is to modify the gain of one of the components in each color difference si~nal, such as the luminance component Y or the color component R in the R-Y signal, whereby the color difference signals become zero. In the embodiment shown in FIG. 1, the level ~ -8-t;3~3~

of the luminance component Y is adjusted, and the adjusted lumi-nance component then is added to each of the color difference si~nals so that the resultant color difference signal is zero.
Once this white balance is attained, the level adjustment to the luminance component, for example, the gain of an amplifier which is used to adjust the luminance component level, is stored and used when further scenes are viewed or televised by the camera apparatus.
Channels 20R and 20B are substantially the same. Hence, in the interest of brevity, only channel 20R is shown and described in detail. A level adjustment circuit 21, such as an automatic gain control (AGC) circuit has an input connected to terminal 8 for receiving the luminance component Y and an output connected to a combining circuit 29. AGC circuit 21 additionally includes a control input to which a gain controlling signal is supplied.
Combining circuit 29 is an algebraic adding circuit having one input connected to the out~ut of AGC circuit 21, as aforesaid, and another input connected to receive the color difference signal, such as R-Y, from color decoder 4. The output of combining circuit 29 is connected to an output terminal 25R to supply a white-balanced color difference signal thereto. When a white object is viewed by the camera apparatus, such as a white wall, a white building, a snowfall, or the like, the luminance component Y derived at termi-nal 8 has its level corresponding to the white level, and each of the color difference signals produced b~ color decoder 4 likewise correspondfi to the viewed white object. For proper white balance, each color difference signal should be equal to zero. If, for example, the color difference signal R-Y is not equal to zero, then an adjustment should ~e made in order to restore proper white balance. AGC circuit 21 is controlled by the control signal applied ~ 63~

thereto to vary the level of the luminance component Y to produce a modified luminance component ~Y. When this modified luminance component ~Y is added to the color difference signal R-Y, the resultant combined signal (R-Y+ ~Y) becomes equal to zero. Hence, white balance is restored. Stated otherwise, the output of combin-ing circuit 29 is equal to a white-balanced color difference signal.
If the control signal which is applied to AGC circuit 21 is stored for further use, then when the camera apparatus is used to view different scenes, that is, objects other than a white reference object, the color difference signal R-Y produced by combining circuit 29 and supplied to output terminal 25R always will be a proper white-balanced color difference signal.
Channel 20B functions in an analogous manner to derive a white-balanced color difference signal B-Y at output te~inal 25B.
That is, luminance component Y is applied to an input terminal b in each of channels 20R and 20B for AGC operation thereon by AGC
circuits 21 in each channel. Of course, the control signal applied to each AGC circuit may differ from each other, in accordance with the level of the color difference signals produced by decoder 4.
Nevertheless, when the level-adjusted ltlminance component ~ Y is combined with each of the color difference signals, the color difference signal outputs at output terminals 25R and 25B will be properly whîte balanced.
The apparatus whicK is used in channel 20R (and also in channel 20B) for producing and supplying a proper gain control signal to ACC circuit 21 is comprised of a clamp circuit 11, a sample and hold circuit 12, averaging circuits 17 and a memory circuit 30R (30B in channel 20B). Clamp circuit 11 i5 coupled to the output of combining circuit 29 ~ an amplifier 26 and is provided for eliminating a level change resulting from a change 63~;~

of the dark current in camera tube 3. The output of clamp circuit 11 is connected to sample and hold circuit 12 which functions to sample the level of the color difference signal during a white balance adjustment operation. Since the color difference signal which is supplied to the sample and hold cir-cuit is derived from the output of combining circuit 29, this color difference signal is referred to herein as the white-balanced color difference signal. As mentioned above, the white-balanced color difference signal is equal to 2ero when a proper white balance is attained. Accordingly, if the white-balanced color difference signal is not equal to zero, then this output of combining circuit 29 may be considered as an error sig-nal SER. The function of channel 20R, as well as channel 20B, is to reduce the error signals SER and SEB to zero.
The output of sample and hold circuit 12, that is, the samp~d white-balanced color difference signal, or sampled error signal SER, is coupled to averaging circuits 17. The averaging circuits function to eliminate spurious changes in the sampled error signal produced by sample and hold circuit 12. If desired, averaging circuits 17 may be omitted.
As shown in FIG. 1, the output of sample and hold circuit 12 is supplied through averaging circuits 17 to a memory device 30R. This memory device, shown in greater detail with respect to FIG. 4, includes a counter control circuit 40R, a digital counter 5aR, and a digital-to-analog (D/A) converter 51R. The function of memory device 30R is to produce the aforedescribed control sig-nal which is applied to AC~ circuit 21. This control signal is produced as a function of the sampled error signal ~ER and deter-mines the amount of adjustment to the luminance component level which is needed to reduce the sampled error signal to zero. Once fi3~2 the sampled error signal is reduced to zero, or approximately to zero, the control signal which is produced to achieve this opera-tion is stored in memory device 30R and is used as the gain control signal for the luminance component for further usage of the video camera apparatus.
As mentioned above, sample and hold circuit 12 is operable to sample the white-balanced color difference signal produced by combining circuit 29, that is, the error signal SER, when the camera apparatus views a white object. Accordingly, the sampling signal which is supplied to the sample and hold circuit is produced when the luminance component Y is of a level corresponding to the white level. If the white object which is viewed by the camera apparatus is uniformly white over an entire video field or frame, then the sampled signal can be produced during any one or more lS horizontal line intervals in that field or frame. However, it is known that a video image is most stable at the middle portion of the video picture. Thus, it is preferred that the sampling signal be produced when the middle portion of the video picture is at the white level. These conditions for generating the sampling signal are satisfied by the illustrated sampling signal generator comprised of a window pulse generator 15, an adding circuit Z2 and a detecting circuit 14.
Window pulse generator lS is supplied with the horizontal and vertical drive signals HD and VD produced by synchronizing signal generator 9 and is adapted to generate a pulse PW of pre-determined amplitude and duration. Referring to FIG. 2, let it be assumed that the ~ideo picture of an object viewed by the camera appara~us is as shown by the outer rectangular shape formed of a solid l;ne. A more sta~le portion of this video picture is enclosed within the broken rectangle 13. Now, wîthin this more stable 3~Z

rectangular portion, a horizontal line interval which occurs during the middle portion of the video picture can be assumed to be the most stable. The purpose of window pulse generator 15 is to generate pulse PW during the central portion of the horizontal line interval which occurs in the middle portion of rectangle 13. For this purpose, window pulse generator 15 may include counting circuits which serve to count the hori-zontal drive signals following a vertical synchronizing signal to detect when the camera apparatus scans the middle portion of rectangle 13. Thus, after a predetermined count of horizontal drive signals is attained, pulse PW is generated, as by trigger-ing a monostable multivibrator.
Let it be assumed that the horizontal line interval corresponding to the middle portion of rectangle 13 is repre-sented by the luminance component Y shown in FIG. 3A. Windowpulse generator 15 detects when this horizontal line interval is being scanned to produce the window pulse PW shown in FIG. 3B.
As illustrated therein, pulse PW is generated during the central portion of the horizontal line interval shown in FIG. 3A, and exhibits a predetermined duration and amplitude. This window pulse PW is supplied to one input of adding circuit 22, and another input of adding circuit 22 is connected to processing circuit 7 for receiving the luminance component Y tFIG. 3A~.
~dding circuit 22 sums the luminance component Y and the window pulse PW to produce a summed signal SA, shown in FIG. 3C. That is, summed signal SA is formed by the superposi-tion of pulse PW and luminance component Y. This summed signal 5A is supplied to detecting circuit 14. The detecting circuit is provided with a threshold level L corresponding to a white level. If the summed signal SA exceeds thres~old level L, 3~:~

detecting circuit 14 generates an output sampling pulse Ps~ as shown in FIG. 3D. As one embodiment thereof, detecting circuit 14 may be formed of a Schmitt trigger or other threshold detector capable of sensing when summed signal SA exceeds the threshold level L. In addition, a blanking signal PB, produced ~y conven-tional circuitry, is supplled to detecting circuit 14 to prevent the detecting circuit from responding to signals during horizontal and vertical blanking intervals.
It is appreciated that window pulse PW is produced during each field or frame interval of the video signals produced by the ' camera apparatus. That is, one window pulse PW may be produced during each field interval or, if desired, one window pulse may be produced during each frame interval. In addition, threshold level L is set high enough such that detecting circuit 14 does not generate a sampling pulse PS in the absence of a window pulse Pw~ even if the luminance component Y itself corresponds to a white level. That is, threshold level L is hi~her than the maxi-mum level of the luminance component in the absence of the super-position o window pulse Pw~ This means that sampling pulse PS
is produced only during the central portion of the middle of each video picture. That is, sampling pulse PS is produced only during the middle portion of a predetermined horizontal line interval during each field or frame interval, provided the luminance com-ponent during that horizontal line interval corresponds to the white level. Hence, sampling pulse PS has a repetition frequency equal to the vertical drive frequency.
It is appreciated that the red error signal SER produced at the output of combining circuit 29 is sampled during each field or frame interval ~y sampling pulse Ps~ If this sampled level differs from zero, that is, the proper level for white balance, 63~2 memory device 30R supplies a suitable gain control signal to AGC circuit 21 for adjusting the level of the luminance component ~ which is combined with the color difference signal R-Y in com-bining circuit 29. Thus, the level of the error signal SER
correspondingly is adjusted. At ~he next sampling time repre-sented by the next sampling pulse Ps~ the adjusted error si~nal is sampled, and this sampled level again is examined to determine if it is equal to the desired zero level. If not, the control signal supplied to AGC circuit 21 is further modified, resulting in yet a further adjustment in the level of the luminance com-ponent Y fed back to and combined with the color difference signal R-Y. At each sampling interval, this operation is repeated until the error signal SER is equal to the desired zero level. At that time, the control signal supplied to AGC circuit 21 is maintained constant and stored in memory device 30R. This control signal then is used to adjust the level of the luminance component for all further usage of the camera apparatus, thereby resulting in a proper white-balanced color difference signal R-Y at output terminal 25R. A similar operatIon is perormed in channel 20B, resulting in a proper white-balanced color difference signal B-Y
at output terminal 25B.
Since the luminance component Y which is used in producing the sampling pulse PS for channel 20R is the same luminance compo-nent which is used in determining the sampling pulse PS for channel 20~, it is appreciated that sampling pulse PS may be supplied in common to terminal a in each of channel 20R and channel 20B.
That is, a separate sampling pulse generator need not be provided for each channel. Of course, if desired, such separate sampling pulse generators can be used.

~J.~63~

One advantage of using avera~e circuits 17 now will be described. Let it be assumed that the luminance component Y produced during the horizontal line interval corresponding to the central portion of the ~ideo picture includes a deviating portion shown by the broken line in FIG. 3A. When window pulse PW (FIG. 3B) is superposed onto the luminance component Y, the resultant signal Yl includes the deviating portion shown by the broken line in FIG. 3C. If this deviating portion of the super-posed signal is less than the thxeshold level L, then detecting circuit 14 generates a sampling pulse PS which appears as two successive sampling pulses, represented by the broken lines in FIG. 3D. This means that sample and hold circuit 12 is supplied with two sampling pulses to produce two successive samples of the error signal SER. It is e~pected that, in some instances, these successive sampled levels of the error signal are not equal to each other. However, averaging circuits 17 average these successive samples to supply a substantially single sampled level of the error signal to memory device 30R. Hence, averaging circuits 17 function to "smooth" disturbances, abrupt changes or spurious samples of error signal SER.
Referring now to FIG. 4, there is illustrated a logic diagram of one embodiment of memory device 30R. Counter control circuit 40R is comprised of a window comparator for determining if the sampled error signal SER is within an amplitude-window.
That is, the window comparator functions to detect when the sampled error signal is within a predetermined range of amplitude.
This window comparator includes a first comparator 41R, having a non-inverting (~+~ input and an inverting (-) input, and a second comparator 42R also including non-inverting and inverting inputs.

3~?~

A relatively high reference level VH is provided at input terminal 44a and is supplied to the non-inverting input of comparator 41R. A relatively low reference level VL is pro-vided at input terminal 44c and is supplied to the inverting input of comparator 42R. The inverting input of comparator 41R is connected in common with the non-inverting input of comparator 42R to input terminal 44b which, in turn, is con-nected to averaging circuits 17 for receiving the sampled error signal SER-Comparator 41R functions to compare the sampled error signal level SER to the high reference level VH. If the sampled error signal exceeds the high reference level, comparator 41R
produces an output signal Sc of one polarity or amplitude. If the sampled error signal is less than the high reference level, output signal Sc is of an opposite polarity, or is of a differentamplitude. For a purpose soon to be described, signal Sc is designated a count direction signal. In the embodiment shown herein, count direction signal Sc is a count-up signal if VH ~SER, and is represented as a binary "1". Conversely, count direction signal Sc is designated as a count-down signal, and is represented as a binary "0" if SER > VH. Accordingly, and as may be appreciated, comparator 41R may be a differential amplifier, an operational ampli-fier, or any other conventional comparing circuit.
Comparator 42R is substantially similar to comparator 41R
and produces an output signal, represented as a binary "1" if S R > VL This output signal produced by comparator 42R is repre-E

sented as a binary "0" i~ SER < ~L As will be described, theoutput signal produced by comparator 42R is used to enable or inhibit a counting operation.

63~2 Counter control circuit 4~R additionally includes a coincidence circuit, such as an AND gate 43R having inputs con-nected to the outputs of comparators 41R and 42R, respectively.
AND gate 43R produces an output signal Ss which functions to control counter 50R. In particularly, if signal Ss is a binary "1", counter 50R is inhibited. Conversely, if signal Ss is a binary "0", then counter 50R îs enabled.
Counter 50R is an UP/DOWN counter having respective input terminals A, B, C and D. Input terminal A receives the count direction signal Sc, and input terminal C receives clock pulses PC provided by a suitabLe source (not shown). Countex 50R is adapted. to count clock pulse~ PC in an upward direction, that is, to increase the count thereof, in the event that count direction si~nal Sc is a binary "1". Conversely, the counter counts clock pulses PC in a downward direction, that is, to decrement the count thereof, in the event that count direction signal Sc is a binary "0".
Input terminal B of counter 50R is coupled to AND gate 43R via an OR gate 45R. If the signal supplied to input terminal B of the counter is a binary "0", for example, if signal Ss is a binary "0", counter 50R is enabled to count clock pulses PC in the direction determined by count direction signal Sc. If the signal supplied to input terminal B is a binary "1", then counter 50R is inhibited from counting further clock pulses Pc~
Counter 50R is adapted to be preset, or loaded, with a predetermined count, for a purpose soon to be described. Accord-ingly, a pr~determined count ~enerator 53R is coupled to counter 50R. Input terminal D of counter 50R is supplied with a load pulse Pp which, when present, loads counter 50R with the predetermined count supplied thereto by generator 53R. Load puls~ Pp is generated 63~

by a monostable multivibrator 55 which is triggered when a white balance operation is initiated, as will be described.
Thus, it ;s appreciated that counter 50R may be a plural stage digital counter, or register, having its individual stages coupled to predetermined count generator 53R for receiving the predetermined count generated by this generator in response to load pulse Pp. Since such a counter is well known, in the interest of brevity, further description thereof is not provided.
The output of counter 50R is supplied to D/A converter 51R for conversion to a corresponding analog signal which, in turn, i5 supplied from the output terminal 52R of the D/A con-ver~er to AGC circuit 21.
A manually operable switch SW is shown diagramatically as including a movable contact which is selectively engageable with fixed contacts m and 1. Contact m is supplied with a suit-able operating potential +B, and contact 1 is supplied with a reference potential, such as ground. When the movable contact of switch SW engages contact m, a binary "1" is supplied from switch SW to OR gate 45R and, additionally, to monostable multi-vibrator 55 r~hen the movable contact of the switch engagescontact 1, a binary "0" is supplied to OR gate 45R and to the monostable multivibrator. Switch SW is operated by an operator of the white balance adjustment apparatus for the purpose of initiating a white balance adjustment operation. To initiate this operation, the movable contact of switch SW is moved from contact m to contact 1, thereby triggering monostable multivibrator 55 to 5uppl~ load pulse Pp to input terminal D of counter 50~.
At the completion of the white balance ad~ustment operation, the movable contact of the switch engages contact m, thereby inhibiting further adjustment. Although switch SW has been described as a 3~;~

manually operable switch, it is appreciated that, if desired, the aforedescribed switching functian can be achieved automati-cally.
The operation of memory dev;ce 30R, as shown in FIG. 4, now will be described. As described previously, proper white balance is achieved when the level of error signal SER, that is, the level of the white-balanced sampled color difference signal, is approximately zero. In accordance with one aspect of the present invention, window comparator 40R functions to determine when the level of error signal SER is within a narrow range about zero. ~ccordingly, the respective hi~h and low reference levels VH and VL are selected to define this narrow range both above (postive) and below (negative) zero. Thus, the logic opera-tion performed by window comparator 4OR is represented by the following table:

Output of Count Input Level Sc (42R)ss Operation . _ ~ _ .
ER~ H low high low DOWN
. . . .. _ . .
VL SER VH hîgh high high Stop . . . .
ER ~VL high low low UP

The clock pulses Pc,which are counted by counter S~R
in response to the count direction signal Sc and the inhibit/
enable signal Ss,have a frequency equal to the frequency of the sampling pulses Ps~ Thus, clock pulses PC have a frequency equal to the vertical drive frequency, or 60Hz.

~J.~63~

A5 an ex:ample, let it be assumed that the sampled error signal level SER exceeds the range, or window, defined by refer-ence levels VH and VL. Accordingly, count direction Sc is a binary "0", thereby establishing a count-down direction for counter 50R. If i.t is assumed that clock pulse PC is produced subsequent to sampling pulse Ps~ then the count of counter 5QR
is decremented by one cloc~ pulse. This decremented count is converted to a corresponding analog level by D/A converter 51R, and this analog level is supplied as a gain control signal to AGC circuit 21. Hence, the level of luminance component Y is correspondingly adjusted by AGC circuit 21, and this adjusted luminance component level is combined with color difference sig-nal R-Y in combining circuit 29. This reduces the level of error signal SER. At the occurrence of the next sampling pulse Ps~ the reduced level of error signal S~R is supplied to window comparator 40R, and this sampled level is compared to the window defined bv reference levels VH and VL. If the adjusted error signal still exceeds this window, counter 50R counts down in response to the next clock pulse PC to further decrement its count. This decre-mented count again is converted to a corresponding analog signalby D/A converter 51R, and the analog signal is supplied as a gain control signal to AGC circuit 21. Hence, the level of luminance component Y is further adjusted and combined with color difference signal R-Y in combining circult 29 to further reduce the level of error signal SER. The foregoing operation is repeated until the level of the sampled error signal SER is reduced sufficiently to fall within the window defined by reference levels VH and VL. At that time, each of comparators 41R and 42R produces a binary "1", so as to energize AND gate 43R to produce a ~inary "l" inhibit sig-nal Ss. This inhibit sîgnal is transmitted through OR gate 45R to 63~t2 input terminal B of counter 50R, thereby inhibiting further operatîon of the counter. Thus, the last-attained count of the counter is stored therein, and this stored count is used as the gain control signal for establishing the gain of AGC
circuit 21. That is, the count now stored in counter 50R is sufficient to establish the gain of AGC circuit 21 to a level whereby error signal SER îs zero, which, in turn, represents a proper white balance. This stored count is used to maintain the gain of AGC circuit 21 at all times during further opera-tion of the camera apparatus. Consequently, such further opera-tion will be carried out with proper white balance.
It may be appreciated that, if the level of the sampled error signal SER is below the window established by reference levels VH and VL, then count direction signal Sc is a binary "1"
lS to establish a count-up direction for counter 50R. Furthermore, comparator 42R produces a binary "0" which inhibits AND gate 43R
from producing an inhibit signal Ss. Assuming that switch SW
is operated to its "adjustment" condition, whereby the movable contact thereof engages contact 1, a binary "0" is supplied to each input of OR gate 45R. Hence, terminal B of counter 50R
receives a binary "0", or a count-enable signal. A clock pulse PC is counted by counter 50R, whereby the count thereof is incre-mented. This count is converted to an analog signal by D/A con-verter 51R and is supplied as a gain control signal to AGC circuit 21. Thus, the level of luminance component Y is adjusted, and this adjusted component is combined with color difference signal R-Y in combining circuit 29 to increase the level of error signal SER. At the next sample interval, the modified error signal SER

is sampled, and the modified sampled level is co~pared to the window defined by reference levels VH and VL. If error signal SER is still below the window, counter 50R counts the next clock pulse PC
in an upward direction. This operation is repeated until the level of the error signal SER is increased sufficiently to fall within the window defined by reference levels VH and VL. At that time, comparators 41R and 42R each produce a binary "1", whereby AND gate 43R produces the inhibit signal Ss, which is supplied as a binary "1" through OR gate 45R to terminal s of counter 50R. Consequently, counter 50R terminates further count-ing, and the last-attained count is stored therein and used as a control signal to establish the proper gain of AGC circuit 21.
Thus, further operation of the camera apparatus is carried out with proper white balance.
It is preferred to provide a window, or "dead band"
for error signal SER, rather than merely comparing the level 15 of the error signal to a zero level. This is because it is expected that error signal SER may differ by only a small amount from zero, yet still represent a proper white balance. In the absence of this window or dead band, if the error signal is slightly greater than zero, counter 50R Will count down, resulting in a control signal which is used to reduce the level of the error signal.
This reduction in the error signal level may result in an error signal which is less than zero. Consequently, counter 50R will count up to produce a control signal which is used to increase the level of the error signal. This continuous fluctuation in the level of the error signal, which both causes and results in the up and down counting of counter 50R, is unstable. Such unstable operation ~f the gain control circuit results in erroneous opera-tion and improper white balance control. For these reasons, it is preferred to establlsh a window or dead band within which error signal SER is driven. Once the error signal falls within this dead 3~Z

band, further operation of counter 50R is inhibited because a satisfactory white balance is achieved.
Although the aforedescribed operation of counter 50R
may proceed from, for example, a zero count, it is preferred that, when a white balance adjustment operation is to be per-formed, the predetermined count provided by generator 53R is loaded into counter 50R. Th;s can be best understood by refer-ence to the graphical depiction shown in FIG. 5 wherein the abscissa represents the count of counter 50R and the ordinate represents the control signal supplied to AGC circuit 21 by D/A converter 51R. It is possible that, in response to a pre-viou~ white balance adjustment operation, the count stored in counter 50R corresponds to a minimum gain control signal ~Vm.
However, when the next white balance adjustment operation is performed, it may be necessary to change the count of counter 50R until a maximum gain control signal +Vm is produced. This means that the count of counter 50R must be changed from a minimum count to a maximum count. This, of course, requires a considerable amount of time, especially since the count of counter 5aR is changed by only one clock pulse at a time.
Furthermore, the count of counter 50R, as well as the level of the gain control signal, must pass through an intermediate count M, corresponding to a zero gain control signal.
Taking the foregoing into consideration, it is appre-ciated that, at the start or initiation of a white balance adjust-ment operation, if the count ~ is preset, or loaded into counter 50R, this could significantly reduce the amount of time needed to complete the white balance adjustment operation. In accordance with the aforedescribed example, the maximum time required to change the AGC control signal from ~Vm to +Vm is the time required to change the count of counter 50R from M to a maximum count, i3~

rather than from a minimum count to a maximum count. Hence, by presetting counter 50R to an intermediate count M, the time re~uired to complete the white balance adjustment opera-tion can be reduced by up to one-half the time that would be necessary in the absence o~ predetermined count generator 53R.
As another example, if the immediately preced,ng count stored in counter 50R is equal to the count A (FIG. 5), and if this count must be changed to count B in order to adjust the white balance properly, for e~ample, in the event of a change in the lighting condition, then it is seen that the time required to change the count from a preset count M to desired count B is substantially less than the time required to change the count of counter 50R from count A to count B. Here again, the time for adjusting the white balance is significantly reduced by pre-setting the count of counter 50R to the intexmediate count M.
When the video camera apparatus is used normally fortelevising a scene, switch SW is set to its normal condition whereby the movable contact engages contact m. Consequently, a binary "1" is supplied through OR gate 45R from switch SW, thereby inhibiting counter 50R from counting clock pulses PC.
This means that the last-attained count of the counter is stored therein and is used as the gain control signal for ~GC circuit 21.
If an operator wishes to adjust the white balance, switch SW is operated to its adjustment condition, whereby the movable contact thereof engages contact 1. Thîs supplies a binary "0" to OR gate 45R, thereby conditioning the OR gate to respond to the count inhi~it or enable signal Ss supplied thexeto by AND gate 43R.
In addition, the negative transitîon in the signal produced by switch SW when switched to its adjustment condition triggers mono-stable multivibrator 55 to produce load pulse Pp. This loads 63~:

counter 50R with the preset count supplied thereto by predeter-mined count generator 53R. Hence, the counter is preset to the aforedescribed intermediate count ~, and th.en counts clock pulses PC either in an upward or downward direction depending upon count direction signal Sc. As is now recognized, this counting of counter 50R changes the gain control signal supplied to AGC cir-cuit 21 in a direction to modify error signal SER until this error signal exhibits a substantially zero level. That is, counter 50R continues to count until error signal SER is within the dead band established by reference levels VH and VL.
In the embodiment shown in FIG. 4, the last-attained count reached by counter 50R when inhibit signal Ss is applied to input terminal B is stored in the counter and is used there-from to derive the gain control signal. In an alternative embodi-ment, a separate stora~e register may be provided to receive thelast-attained count reached by counter 50R. Suitable gating circuits can be interposed between counter 50R and this storage register, the gating circuits ~eing energized in response to an inhibit signal Ss or in response to a binary "1" produced by switch SW when switched from lts adjustment condition to its normal condition. The count then stored in th.is separate regis-ter can ~e converted to an analog signal by D/A converter 51R
and supplied a,s th.e gain control signal to AGC circuit 21. For the purpose of the present discussion, counter 50R, by itself, or th.e additional inclusion of such a separate storage register may be considered as part of the counting circuit shown in FIG. 4.
Turning now to FIG. 6, there is illustrated a logic diagram of a memor~ device 30R and a memory device 3QB which are included in channels 20R and 20B, respectively ~FIG. l).

Each of these memory devices is seen to be substantially identical 63~'~

to the memory device shown and described hereinabove with respect to PIG. 4. Accordingly, like component parts shown in FIG. 6 are identified with the same reference numerals as used in FIG. 4.
In addition, the componen~ compris;ng memory device 30B are iden-tified with the same reference numerals as used to identify thesimilar components of memory device 30R, except with the addi-tional suffix "B". Furthermore, clock pulses PC are seen to be supplied to input terminals C of both counters 50R and 50B.
Similarly, load pulses Pp are applied to input terminals D of both counters 50R and 50B. This means that both counters are preset with respective predetermined counts, as supplied thereto by predetermined count generators 53R and 53s, respectively.
Still further, a single switch SW is shown in FIG. 6, this switch being coupled to OR gates 45R and 45B to the B inputs of counters 50R and 50B, respectively. Hence, some of the cir-cuit elements previously discussed with respect to FIG. 4 can be used in common with both memory devices 30R and 30B.
FIG. 6 additionally includes an indicator for providing an indication when proper white balance has been achieved. This indicator is comprised of an AND gate 60 whose output terminal 61 is connected to a visual indicator 62. AND gate 60 includes a pair of inputs connected to the outputs of AND gates 43R and 43B, respectively, to receive inhibit signals SsR and SsB.
Visual indicator 62 may comprise any suitable light source, such as an LED, or the like. It is recalled that, when error signal SER has been sufficiently modified so as to fall within the window defined by reference levels VH and VL, then the color difference signal R-Y derived at the output of combining circuit in channel 20R is properly white balanced. When this occurs, inhibit signal SsR is a binary "l". It is appreciated that when the blue error 1~.;263~

signal SEB fall~ within the window defined by reference levels VH and VL in channel 20s, t~en the color difference signal s-Y
derived at the output of t~e combining circuit included in this channel likewise is properly white balanced. T~hen this occurs, inhibit signal SsB also is a binary "1". AND gate 60 detects the coincidence of a binary "1" in each of these inhibit signals to energize visual indicator 62. Thus, when indicator 62 is energized, each of color difference signals R-Y and B-Y is within its respective window, corresponding to a proper white balance.
Consequently, an operator can easily and rapidly detect when a white balance adjustment operation is complete. When indicator 62 is energized, switch SW then can be switched from its adjust-ment condition to its normal condition. Color video sianals subqequently produced by the video camera apparatus will, of course, be properly ~hite balanced.
The embodiment shown in FIG. 6 also provides an indica-tion of the color temperature of white unbalance. As is known, if the lighting condition of an object is of a relatively high color temperature, then the red color difference R-Y is less than zero, that is, it is negati~e, while the blue color differ-ence signal B-Y is greater than zero, that is, it is positive.
Conversely, if the lighting condition of an object is of a relatively low color temperature, then the red color difference signal R-Y i5 greater than zero, or positive, while the blue color difference signal B-Y is less than zero, or negative.
These color temperature conditions are indicated by circuits 80 and 70, respectively. That is, circuit 80 includes an output terminal 83 whereat a binar~ "1" is produced if the color tem-perature of an illuminated object is high; and circuit 70 includes an output terminal 73 whereat ~ ~inary "1" is produced in the 1~.2f~3~z event that the color temperature of an illuminated object is relatively low.
Circuit 80 includes logic inverters 81A and 81B con-nected to the outputs of comparators 42R and 41B, respectively.
The outputs of inverters 81A and 81B are connected to respective inputs of an OR gate 82 whose output is connected to output terminal 83. Circuit 70 is o simila~ construc~ion and includes inverters 71A and 71B connected to the outputs of comparators 41R
and 42B, respectively. The outputs of inverters 71A and 71B are connected to respective inputs of OR gate 72 whose output is connected to output terminal 73.
If the color temperature of the illuminated object is high, then the color difference signal R-Y is less than reference level VL. This means that the output of comparator 42R i5 of negative polarity. Inverter 81A inverts this negative polarity to supply a binary "1" through OR gate 8~ to output terminal 83, thereby indicating a high color temperature. Also, for a high color temperature, the blue color difference signal s-Y exceeds reference level VH, resulting in a relatively negative signal at the output of comparator 41B. This negative signal is inverted by inverter 81B to supply a binary "1" through OR gate 82 to out-put terminal 83, thereby indicating the high color temperature.
For a low color temperature, the red color difference signal R-Y exceeds reference level VH. This condition results în a relativeIy negative signal at the output of comparator 41R.
Inverter 71A inverts this signal to a binary "1" which is supplied through OR gate 72 to output terminal 73, thereby providing an indication of the low color temperature. Also, a low color tem-perature is represented by the blue color difference sIgnal B-Y

being less than reference level VL. This condition results in a ~63~3~

relatively negative signal at the output of comparator 42B.
Inverter 71B inverts this signal to a binary "1" which is supplied through OR gate 72 to output terminal 73.
Thus, if a white balance cannot be attained, an operator readily may determine the reason for this loss of white balance. If either circuit 70 or circuit 80 produces a binary "1" at its respective output terminal, an operator will be a~prised of the relative color temperature of the illuminated object and will recognize that a color temperature correcting filter either should be added or changed. Suitable display lamps, LED's, or other indicators may be connected to output terminals 73 and 83 to provide the respective low and high color temperature indications to the operator.
Thus, hy providing indlcator 62 and color temperature indicating circuits 70 and 80, an operator, such as a cameraman, will be supplied with information apprising him as to the white balance condition of the camera apparatus and, if necessary, the need for color temperature filter correction. Hence, the cameraman will be enabled to rapidly and efficiently adjust the white balance of the video signals correctly.
While the present invention has been particularly shown and described in the environment of a white balance control system for use in video camera apparatus, it should be readily appreciated that the memory-type control system disclosed herein admits of various other uses. For example, the embodiment shown in FIG. 4 can be used as a memory-type automatic frequency control (AFC) system, an automatic phase (APC) system, or the like. Still further, this invention can be used in other feedback or servo control environments whereby a control signal is produced and stored in digital form for subsequent use 63~

to control any predetermined parameter of an input signal.
It will be readily apparent to those of ordinary skill in the art that various changes and modifications in form and details in addition to those changes noted hereinabove can be made wîthout departing from the spirit and scope of the invention. Therefore, it is intended that the appended claims be interpreted as including such changes and modi~ications.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A memory-type white balance control system for controlling the white balance of color video signals produced by video camera apparatus, comprising:
means for producing color difference signals correspond-ing to an object viewed by said camera apparatus;
means for producing a component of said color difference signals;
combining means for combining said component with said color difference signals to produce white-balanced color differ-ence signals;
sensing means for sensing when the object viewed by said camera is a white object;
detecting means responsive to said sensing means for detecting when the level of a white-balanced color difference signal is within a predetermined range;
a source of clock pulses;
UP/DOWN counting means for counting said clock pulses, said UP/DOWN counting means being responsive to said detecting means for counting in one direction when said level of said white-balanced color difference signal is greater than said predetermined range, for counting in a second direction when said level is less than said predetermined range and for ceasing said counting when said level is within said predetermined range so as to store the last-attained count; and automatic gain control means responsive to the count of said counting means for controlling the level of said component which is combined with said color difference signals.

2 . The system of Claim 1 further comprising actuable switch means having a first condition for inhibiting the count to which said automatic gain control means is responsive from chang-ing and a second condition for permitting the count to which said automatic gain control means is responsive to change.

3. The system of Claim 2 wherein said actuable switch means comprises a manual switch.

4. The system of Claim 2 further comprising means for providing a pre-set count; and means responsive to the actuation of said switch means from the first condition to the second condi-tion thereof for loading said pre-set count into said counting means.

5. The system of Claim 1 wherein said detecting means comprises sampling means for sampling said white-balanced color difference signal when said sensing means senses that the object viewed by said camera is a white object; comparator means for comparing the sampled white-balanced color difference signal to a high reference level and to a low reference level to produce a count-down signal if said sampled white-balanced color difference signal exceeds said high reference level and a count-up signal if said sampled white-balanced color difference signal is less than said high reference level, and to produce a count-enable signal if said sampled white-balanced color difference signal is less than said low reference signal and a count-inhibit signal if said sampled white-balanced color difference signal exceeds said low reference signal; and coincidence detecting means for detecting the coincidence of said count-up and said count-inhibit signals so as to inhibit further counting by said counting means.

6. The system of Claim 5 wherein said sensing means comprises pulse generating means for generating at least one pulse of predetermined amplitude and duration during a preselected portion of each frame interval of the video signals produced by said camera; means for superposing said pulse and said component of said color difference signal; and sampling signal generating means for supplying a sampling signal to said sampling means when the superposed pulse and component exceeds a threshold level.

7. The system of Claim 6 wherein said component is a luminance signal Y and said color difference signal is the dif-ference between a color signal R, G or B and said luminance signal Y.

8. A memory-type white balance control system for controlling the white balance of color video signals produced by video camera apparatus, comprising:
means for producing first and second color difference signals corresponding to an object viewed by said camera apparatus;
means for producing a component of said color difference signals;
sensing means responsive to the level of said component for sensing when the object viewed by said camera is a white object;
first and second combining means for combining said component with said first and second color difference signals, respectively, to produce first and second white-balanced color difference signals;
first and second sampling means responsive to said sensing means for sampling said first and second white-balanced color difference signals, respectively;
first and second range comparators for determining if said first and second sampled white-balanced color difference signals are within first and second amplitude ranges, respectively, to produce first and second count-down signals if said first and second sampled white-balanced color difference signals exceed the upper limits of said first and second ranges, respectively, first and second count-up signals if said first and second sampled white-balanced color difference signals are less than the lower limits of said first and second ranges, respectively, and stop signals if said first and second sampled white-balanced color difference signals are within said first and second ranges, respectively;
a source of clock pulses;
first and second UP/DOWN counting means for counting said clock pulses, said first and second counting means being responsive to said first and second count-down, count-up and stop signals, respectively, for counting in a downward direction, counting in an upward direction and stopping said counting;
first and second automatic gain control means responsive to the count of said first and second counting means, respectively, for controlling the level of said component which is combined with a respective one of said first and second color difference signals; and indicating means responsive to said first and second stop signals for indicating when said first and second white-balanced color difference signals are balanced properly.

9. The system of Claim 8 wherein said indicating means comprises coincidence detecting means for detecting the coincidence of said first and second stop signals; and a visual indicator energized by said coincidence detecting means.

10. The system of Claim 9 wherein said indicating means further comprises means coupled to said first and second range comparators for detecting the relative color temperature of the viewed object in the event that said white-balanced color difference signals are not balanced properly.

11. The system of Claim 10 wherein said means for detecting the relative color temperature comprises means for detecting a relatively low color temperature if said first sampled white-balanced color difference signal exceeds the upper limit of said first range or if said second sampled white-balanced color difference signal is less than the lower limit of said second range; and means for detecting a relatively high color temperature if said first sampled white-balanced color difference signal is less than the lower limit of said first range or if said second sampled white-balanced color difference signal exceeds the upper limit of said second range.

12. The system of claim 8 wherein said sensing means comprises pulse generating means for generating a pulse of pre-determined duration during a predetermined horizontal line inter-val in a field of the video signals produced by said camera; means for superposing said pulse and said component of said color differ-ence signals; and sample signal generating means for generating and supplying a sampling signal to said first and second sampling means when the superposed pulse and component exceeds a threshold level;
and wherein said source of clock pulses comprises means for supply-ing clock pulses at a frequency synchronized with the vertical synchronizing frequency of said video signals.

13. The system of Claim 12 wherein each of said sampling means comprises sample and hold means responsive to said sampling signal for sampling a respective white-balanced color difference signal and for substantially holding the sampled signal until the occurrence of the next sampling signal; and averaging means for averaging the sampled signals over a duration of time, said averaged sampled signals being supplied to a respective range comparator.

14. The system of Claim 8 further comprising a manual switch operable to be energized for initiating a white balance operation and to be de-energized for terminating said white balance operation; first and second means for providing respec-tive pre-set counts; first and second means responsive to the energization of said manual switch for loading said pre-set counts into said first and second counting means, respectively;
and means for inhibiting further counting of said first and second counting means in response to the de-energization of said manual switch.

15. The system of Claim 8 wherein said first and second color difference signals are R-Y and B-Y signals, respec-tively, and said component is the luminance component Y.

16. A memory-type control system for producing and storing a control signal, comprising:
signal providing means for providing a signal having a level to be controlled;
detecting means receiving said signal to be controlled for detecting when said level is within a pre-determined range;
a source of clock pulses;
UP/DOWN counting means for counting said clock pulses, said UP/DOWN counting means being responsive to said detecting means for counting in one direction when said level is greater than said predetermined range, for counting in the other direction when said level is less than said predetermined range and for ceasing said counting when said level is within said range so as to store the last-attained count;
level control means coupled to said counting means and using said count as a gain control signal to adjust said level so as to bring said level within said predetermined range, said level control means including level adjusting means for adjusting the level of said signal, and digital-to-analog converting means for converting the count of said counting means to an analog level control signal and for applying said analog level control signal to said level adjusting means; and said signal providing means including a source of color video signals representing a white object, means for deriving a color difference signal corresponding to said white object, means for providing a component of said color difference signal, and means for algebraically combining said component and said color difference signal so as to vary the level of said color difference signal, said component being applied to said algebraic combining means through said level adjusting means.